Many scientists contend that release of halogen refrigerants into the atmosphere deleteriously affects the ozone layer that surrounds and protects the earth from ultraviolet solar radiation. Recent international discussions and treaties, coupled with related regulations and legislation, have renewed interest in devices for recovery and storage of used refrigerants from refrigeration equipment for later purification and reuse or for proper disposal. U.S. Pat. No. 4,261,178, assigned to the assignee hereof, discloses a refrigerant recovery system in which the inlet of a compressor is coupled through an evaporator and through a manual valve to the refrigeration equipment from which refrigerant is to be recovered. The compressor outlet is connected through a condenser to a refrigerant storage container. The condenser and evaporator are combined in a single assembly through which cooling air is circulated by a fan. Content of the storage container is monitored by a scale on which the container is mounted for sensing weight of liquid refrigerant in the container, and by a pressure switch coupled to the fluid conduit between the condenser and the container for sensing vapor pressure within the storage container. A full-container condition sensed at the scale or a high-pressure condition sensed at the pressure switch terminates operation of the compressor motor. A vacuum switch is positioned between the inlet valve and the evaporator for sensing evacuation of refrigerant from the refrigeration system and automatically terminating operation of the compressor motor.
U.S. Pat. No. 4,768,347, also signed to the assignee hereof, discloses a refrigerant recovery system that includes a compressor having an inlet coupled through an evaporator and through a solenoid valve to the refrigeration equipment from which refrigerant is to be withdrawn, and an outlet coupled through a condenser to a refrigerant storage container or tank. The refrigerant storage container is carried by a scale having a limit switch coupled to control electronics to prevent or terminate further refrigerant recovery when the container is full. The scale comprises a platform pivotally mounted by a hinge pin to a wheeled cart, which also carries the evaporator/condenser unit, compressor, control electronics, and associated valves and hoses. In the preferred embodiment, the condenser and evaporator are combined within a single assembly, in heat exchange relationship with each other, which also includes oil separation and oil drain facility.
U.S. Pat. No. 4,805,416 discloses refrigerant recovery and purification systems that include facility for operation of the compressor to withdraw recovered refrigerant from the storage container, circulate the refrigerant in a closed path through a filter/dryer, and then return the refrigerant to the storage container. A supplemental condenser may be positioned between the storage container and the primary condenser in the heat-exchange/oil-separator unit to provide enhanced condenser heat-rejection capability, and thereby facilitate extended operation of the unit in the purification mode without overheating the refrigerant or the compressor. All refrigerant from the compressor flows through both the primary condenser and supplemental condenser in both of the recovery and purification modes.
Although the systems disclosed in the noted patents address and overcome problems theretofore extant in the art, and have enjoyed substantial commercial acceptance and success, further improvements remain desirable. In particular, it has been found that, under some operating conditions, there is more heat to be withdrawn from the refrigerant at the condenser than is needed to obtain complete evaporation at the evaporator, leading either to undesirable superheating at the evaporator or less than complete condensation at the condenser. However, under other operating conditions for the same unit, heat exchange at the evaporator/condenser achieves the desired balance. It is therefore a general object of the present invention to provide a refrigerant handling system in which refrigerant flow through the condenser is controlled in such a way as to reduce undesirable superheating at the evaporator while at the same time obtaining maximum available heat withdrawal and condensation of refrigerant at the condenser. A more specific object of the present invention is to provide a system, particularly a refrigerant recovery system of the character described above, that operates at approximately 10.degree. F. superheat at the evaporator, and that maintains refrigerant temperature at the condenser to less than 25.degree. F. above ambient or 45.degree. F. above evaporator temperature as appropriate.